The flavivirus genus is of major concern for world morbidity and mortality and includes viruses causing both encephalitic as well as hemorrhagic diseases. The incidence of Tick-borne encephalitis is increasing in many European countries and several reports have emphasized the expansion of the main vector, Ixodes ricinus. The pattern of vector distribution is also changing in Sweden, which makes it important to set up solid and successful strategies for detection and genetic characterization of novel Swedish TBEV strains. In this study we have generated strategies for detection of broad types of tick-borne flaviviruses in pools of I. ricinus sampled in Sweden. The positive collection on the island of Torö was used to generate a sequence of a complete TBEV genome straight from the arthropod reservoir. This cloned virus was used to construct a self-replicating DNA based sub-genomic TBEV replicon capable of expressing reporter genes. The replicon was used to study the effect of TBEV on neurite outgrowth, which revealed that the MTase domain of NS5 block the formation of the Scribble/Rac1/βPIX protein complex, impairing neurite outgrowth in neuronal growth factor induced PC12 cells. We also demonstrate that TBEV replication is affected by two PDZ binding motifs within NS5 and reveal putative PDZ binding proteins. These interactions might affect cellular pathways and might have a role in flavivirus replication. We also characterize the variable 3´ non-coding region (V3’-NCR) by in silico studies on TBEV. Analysis brings new evidence that V3’-NCR region carries an enhancer element important for different replication/translation dynamics during the viral lifecycle in mammalian and tick cells. We also propose a temperature-sensitive trans-acting riboswitch mechanism; altering the secondary RNA structures of a closed form at lower temperatures and a form open for translation at higher temperatures. This mechanism may explain the low TBEV level observed in sampled ticks. / <p>At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 4: Manuscript.</p>

Powassan (POW) virus, the cause of human encephalitis in the northeastern U.S. and Canada, is transmitted by tick bite. Since the geographic and host distribution patterns of Ixodes dammini Spielman, et al, 1979 and POW virus overlap, the potential of this tick species to transmit POW virus was explored. Transmission experiments were conducted with hamsters and rabbits which fed immature and adult ticks, respectively, from a POW-free colony. Oral infection rates in larvae and nymphs fed on POW-infected hamsters were 10% and 40%, respectively; in females fed on POW-infected rabbits, 57%. Transstadial transmission rates for nymphs exposed to POW virus as larvae, adults exposed as larvae, and adults exposed as nymphs, were 9.5%, 10% and 54%, respectively. Evidence of transovarial transmission was acquired when 2 clean hamsters feeding F$ sb2$ larvae and nymphs originally exposed to virus in the F$ sb1$ nymphal stage seroconverted to POW virus with hemagglutination inhibition titers of 80 and 5120, respectively, on week 4 post-tick-drop-off. The transovarial transmission rate was 16.6%. All developmental stages were able to transmit POW virus orally to clean hosts regardless of when the ticks were originally exposed to virus. / These results indicate that I. dammini is a competent vector of POW virus under experimental conditions. Field studies are necessary to determine if the same holds true under natural conditions.

No description available.

Diss. (sammanfattning) Stockholm : Karol. inst., 2006. / Härtill 5 uppsatser.

No description available.

Tick-borne encephalitis risk assessment based on classification of vegetation from remote sensing data Abstract The main aim of this thesis has been to find out how to classify various categories of forest vegetation with a different risk of exposure to the tick-borne encephalitis based on the Landsat imagery. The legend used here is derived from the one used in the projects by Daniel, Kolář, Zeman (1995) and Daniel, Kolář, Beneš (1999) but has been reduced to only five classses with no overlaps in their definitions (I. coniferous stands, II. mixed stands, III. young deciduous stands and stand ecotones with a highly heterogeneous structure, IV. deciduous stands with a homogeneous structure, V. deciduous stands with a heterogeneous structure). The supervised classification with the Maximum Likelihood Classifier has been used on the Landsat imagery from various seasons. Difficulties concerned with the presence of clouds and varying Sun elevation across the imagery had to be adressed in the course of the work. The training sites and the control points have been defined by the field research and interpretation of the relevant orthophotomaps and Landsat imagery in 5-4-3 RGB composite. The mask of the forest has been created on the ZABAGED data basis. The time horizon of 2006 - 2010 has been the primary focus....

The genomic RNA encoding the structural proteins of louping ill, a tickborne flavivirus, was cloned and sequenced. Sequence comparisons of louping ill envelope protein showed greater homology with tick-borne than mosquito-borne flaviviruses and greater homology with the western than the far eastern subtype of tick-borne encephalitis virus. Louping ill and tick-borne encephalitis viruses are probably varieties of a common tick-borne ancestral virus. The average amino acid sequence diversity between members of the tick-borne serogroup was significantly lower than that of mosquito-borne serogroups, suggesting that tick-borne flaviviruses have been subjected to different evolutionary immune selection pressure from the mosquito-borne viruses. Using the published model of tick-borne encephalitis envelope protein and the derived sequence data on louping ill virus, three discontinuous peptides (amino acids 81-88, 207-212 and 230-234) which may represent critical molecular determinants within the receptor binding site of tick-borne flaviviruses, were identified. These peptides may provide a specific genetic marker for these viruses. Recombinant baculoviruses and vaccinia viruses containing cloned DNA, encoding either the envelope protein or the structural proteins of louping ill virus, were constructed. Glycosylated envelope protein, presented both inside and on the surface of insect and mammalian cells, was expressed by all four recombinant viruses. Differences in antigenic presentation of envelope protein were observed between envelope protein and structural protein constructs as well as between insect cell and mammalian cell expression systems. Despite the expression of epitopes known to elicit neutralizing and protective antibodies when present in authentic antigen, the recombinant envelope protein expressed by either baculovirus or vaccinia virus failed to induce, under the experimental conditions employed, either neutralizing or protective antibodies in both mice and rabbits against louping ill virus. Hence, louping ill envelope protein expressed by baculoviruses and vaccinia viruses was antigenically reactive but immunogenically inert.

The proposed thesis contributes to the knowledge about tick-borne encephalitis and its pathogenesis. The thesis describes pathogenesis and immunopathogenesis of tick-borne encephalitis, impact of host's genotype in clinical course determination, immune response of patients with acute tick-borne encephalitis, the mechanism of tick-borne encephalitis virus migration into central nervous system and virus interaction with cells of neurovascular unit as well as potential medical interventions.

This study was focused on the influence of hard tick from Ixodes ricinus on the replication of tick-borne encephalitis virus in vivo and the on the accompained changes in the levels of inflammatory cytokines which were determined in serum of infected mice. Futher the effect of tick cystatins, the inhibitors of cysteine proteases, on gene expression of interferon regulated factors was investigated in dendritic cells upon stimulation with Toll-like receptor ligands.

Tick-borne encephalitis is a vector-borne zoonotic disease with more than 12,000 annual clinical reported cases globally (WHO, 2021). Tick-borne encephalitis is caused by the flavivirus and transferred by Ixodes ricinus from roe deer to human and affects the central Nervous system. Climate change also increases tick-borne encephalitis incidences in Sweden and fluctuated considerably from year to year. A quantitative study design with secondary data was conducted to analyze the spatial and temporal pattern of Tick-borne encephalitis in Sweden from 1986-2020. The distribution of Tick-borne encephalitis within age and sex, along with other factors were also analyzed. The results showed that Tick-borne encephalitis with passing each year spread across the country. Male and age group, 50-59, have more incidence of Tick-borne encephalitis. Incidents were associated with climate conditions such as temperature and precipitation, which provided a favorable environment for Ixodes ricinus for its lifecycle activities, host searching, and disease transmission. Roe deer population, other vertebrates abundance, vaccination, population interest, economy, and land change are the critical factors that facilitate the disease incidence or control. People who visit forests for hunting, trekking, leisure, and professional activities without proper immunity and preventive measures are at risk to infect with Tick-borne encephalitis. The theory One health approach showed suitable performance for the control of this vulnerable climate zoonotic disease.